Process for the emulsification of polydimethyl siloxane oils, organomodified siloxane oils and organic oil using non-ionic surfactants

ABSTRACT

A process for preparing an oil-in-water emulsion is provided, which process comprises mixing and heating a water-insoluble organomodified polysiloxane oil or an organic oil, an organomodified silicone emulsifier, water and an alkaline metal salt above the cloud point of the emulsifier under agitated conditions and cooling the resulting mixture below the cloud point.

This is a continuation-in-part of Ser. No. 07/801,517 filed Dec. 2, 1991now U.S. Pat. No. 5,234,695.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a process for preparing anoil-in-water emulsion. More particularly, the present invention isdirected to a process for preparing a stable off-in-water emulsion offine particle size which is useful in making emulsions for use in wovenand non-woven textiles, cosmetic, personal care and pharmaceuticalapplications.

2. Prior Art

U.S. Pat. No. 4,620,878 describes a method for making apolyorganosiloxane fine emulsion or microemulsion. In this method atranslucent oil concentrate is prepared. The concentrate is rapidlydispersed in water by the incremental addition of water to theconcentrate to form an oil-in-water fine or microemulsion usinghigh-shear mixing. This patent explicitly teaches: "When a singlenonionic surfactant is employed as the insoluble surfactant, the cloudpoint of the surfactant should be higher than the temperature at whichthe emulsion is prepared." (Col. 9, lines 37-40).

S. Friberg, and K. Shinoda, Emulsions and Stabilization (John Wiley &Sons, 1986), report two distinct methods of emulsion preparation:Emulsification by the Phase Inversion Temperature (PIT) Method andEmulsification by the Inversion Process (IP). PIT emulsificationinvolves preparing an emulsion near (just below) the phase inversiontemperature of the system. The phase inversion temperature is acharacteristic property of an emulsion (rather than of the surfactantalone) at which the hydrophile-lipophile property of the nonionicsurfactant is in balance (i.e., the temperature of the emulsion at whichthe surfactant has an equal affinity for both the oil and water phasesof the emulsion). According to the PIT method, desired emulsions areobtained if an emulsion system is initially emulsified just below thePIT and then cooled rapidly, since interfacial tension is reduced at thePIT and rapid cooling adds small droplets from the initial phaseseparation of the surfactant.

In the IP method of Friberg and Shinoda, emulsification is performed ata temperature higher than the PIT in order to first form a water-in-oilemulsion which then inverts to an oil-in-water emulsion upon coolingbelow the PIT. That is, Friberg and Shinoda emphasize either conductingthe emulsification close to or slightly below the cloud point (PIT) orforming a water-in-oil emulsion at elevated temperature which is theninverted upon cooling (IP).

Surprisingly, it has been found that, by the process of the presentinvention, oil-in-water emulsions are easily obtained without thetemperature constraints of the prior art methods. Further, the degree ofmechanical agitation or work required to prepare the emulsion issignificantly reduced by the process of this invention as compared tothe above-mentioned processes in the art. Additionally, the process ofthe present invention permits the manufacture of emulsions which have alow bio-burden, since the emulsion is optionally pasteurized duringpreparation, thereby reducing the bio-burden that must be overcome bythe addition of antimicrobial preservatives. Further, the process of thepresent invention produces stable (i.e., shelf life or storage life ofat least two weeks) oil-in-water emulsions having a fine particle size.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing an oil-in-wateremulsion comprising mixing and heating (i) a water-insolubleorganomodified polysiloxane oil, (ii) an organomodified siliconeemulsifier, (iii) water, and (iv) an alkaline metal salt, above thecloud point of the emulsifier and cooling the resulting mixture belowthe cloud point of the emulsifier. The mixing and heating steps can becarried out either sequentially or simultaneously.

DETAILED DESCRIPTION OF THE INVENTION The Process of Preparing theEmulsion

In preparing emulsions by the process of the present invention, theorder of addition of the individual components is not critical, and,hence, they can be charged to a mixing vessel in any desired order.Mixing and heating of the components are performed simultaneously orsequentially. Preferably, mixing and heating takes place sequentially.By mixing and heating sequentially is meant that the components aremixed prior to heating.

The components are initially mixed, preferably blended, under agitatedconditions such that a major portion of the non-aqueous components(i.e., the oil and the emulsifier) does not form a visible oil layer onthe surface or top of the mixture or blend, but rather is suspended inthe liquid prior to heating the mixture.

When the components are mixed or blended prior to heating, the rateand/or type of agitation is not critical and is generally less strenuousthan that applied during heating. Any well known means of moving thebulk of the mixture in the vessel is suitable to provide agitation thatis applied prior to heating. Agitation prior to heating is convenientlyand conventionally accomplished by use of, for example, low shear mixing(also known as "bulk mixing") and can be accomplished by use of, forexample, a marine propeller, an anchor style paddle, or flat-bladedturbine. Such low shear mixing or agitation causes a volumetricdisplacement of between about 0.2 liter/minute/liter of mixture up toabout 16 liter/minute/liter of mixture, preferably between about 1 to 10liter/minute/liter of mixture, and, for example, most preferably about2.8 liter/minute/liter of mixture as described by J. Y. Oldshue in FluidMixing Technology (McGraw-Hill, 1983) at page 89.

After the mixing step, or simultaneously along with the mixing, themixture is heated. For the purpose of forming an emulsion, withoutpasteurization of the emulsion, the mixture is heated under agitatedconditions to a temperature of at least 5° C., preferably 10° C., andmost preferably 15° C. or more above the cloud point of thewater-soluble organomodified polysiloxane emulsifier. By "cloud point"is meant the temperature at which one gram of the polysiloxaneemulsifier becomes insoluble in a 99-ml water solution. In general,heating in order to form an emulsion is conducted at the desiredtemperature for a time period sufficient to form the emulsion. Such timeperiod ranges, for example, between about 2 minutes and 2 hours,preferably between about 2 minutes and 1 hour, and most preferablybetween about 5 minutes and 30 minutes. In general, the temperatureduring the heating step ranges from about 25° C. to 100° C., preferablyfrom about 40° C. to 90° C., and most preferably from about 45° C. to70° C.

Agitation during heating in the process of the present invention iscritical and is conducted using any means known in the art to effect theintimate contact of and/or intermingling of the water insoluble phase(i.e., the oil and the emulsifier). For example, high shear mixing oragitation is accomplished by use of a shear type mixer such as a fiatplate impeller with sawtooth edges, a rotor stator mixer, tapered fiatblade radial impeller or bar turbine as described by J. Y. Oldshue inFluid Mixing Technology (McGraw-Hill, 1983) at page 59. Other mechanicalmeans known in the art can be employed to impart the desired shearmixing such as by use of a colloid mill, sand mill, or rotor stator asdescribed by P. Sherman, ed., in Emulsion Science (McGraw-Hill, 1968) atpage 9. When the mixture is heated to the desired temperature, highshear mixing or agitation is applied, for example, to impart a maximumshear rate of between about 450 sec.⁻¹ to 1050 sec.⁻¹, preferablybetween about 500 sec.⁻¹ to 1000 sec.⁻¹, and most preferably betweenabout 650 to 950 sec.⁻¹.

Alternatively, agitation during heating can be described in terms ofimpeller speed. In the process of the present invention, this impellerspeed ranges, for example, from about 2.6 to 12 meters/second,preferably about 5.2 to 7.2 meters/second, and most preferably about 5.5to 7 meters/second.

Heating and agitation of the mixture results in the formation of anoil-in-water gel-like emulsion of small or fine particle size (less thanabout 0.3 microns), as evidenced by a clear to translucent appearanceand a low electrical resistance (less than about 54 kilohms).

Optionally and advantageously, in a preferred embodiment of the processof the present invention, the mixture can be pasteurized. By"pasteurization" is meant the partial sterilization of the mixtureconducted at a temperature and for a period of time, sufficient todestroy objectionable organisms without greatly affecting the chemicalcomposition of the mixture. To achieve pasteurization, a mixture isheated to a desired temperature and maintained at that temperature for aperiod of time sufficient to bring about the destruction of bacteria orother organisms. Time-temperature equivalents necessary to effectpasteurization are well-known in the art and are described, for example,by G. F. Reddish, ed., in Antiseptic, Disinfectants, Fungicides andChemical and Physical Sterilization, 2nd Edition (Lea & Febiger, 1957)at page 958. In general, according to this reference, pasteurizationtakes place, for example, at 60° C. in about 63 minutes or at 80° C. fora time period of at least about 0.4 seconds.

In the process of the present invention, pasteurization takes place aspart of the heating step or as a separate step after the mixture hasbeen heated and/or cooled. Preferably pasteurization occurs as part ofthe heating step. In this latter mode of operation, pasteurizationoccurs at a temperature above the cloud point of the emulsifier. Whenpasteurization is practiced in the process of the present invention, ingeneral, the mixture is heated to about 65° C. to 75° C. for a timeperiod of at least about 6 minutes, preferably about 70° C. to 75° C.for a time period of at least about 38 seconds.

After heating with or without pasteurization, the mixture is cooledbelow the cloud point of the organomodified silicone emulsifier and,more specifically, to ambient temperature. In the process of the presentinvention, the gel which is translucent disperses upon cooling below thecloud point of the organomodified silicone emulsifier without anyagitation. However, while agitation is not required during cooling toproduce the emulsion, some agitation is preferred. The agitation isconveniently provided by means of the aforementioned low shear or (bulk)mixing or volumetric displacement agitation described above to initiallymix or blend the starting components. Agitation during cooling in theprocess of the invention serves to facilitate heat exchange with theenvironment. Another alternative to no agitation or slight agitation(such as low shear mixing), is to continue the high shear mixingconditions employed during the heating step during cooling to facilitateheat exchange or aid in the dispersion of the concentrate or gel phase.Upon cooling, the translucent gel disperses, and an oil-in-wateremulsion is formed. The emulsion is milky white with a blue cast.

Alternatively, in one embodiment of the process of the presentinvention, the ingredients may be mixed such that there exists no freeaqueous phase above the cloud point of the emulsifier. In other words,the quantity of water in the initial mixture is not greater than theamount which is present in the oil-in-water gel that is formed at orabove the cloud point. After completing the mixing and heating asdescribed above to produce the gel, the gel is cooled below the cloudpoint, preferably to ambient temperature. As the gel is cooled, or afterreaching ambient temperature, additional water is added to fore thestable emulsion, preferably a stable fine emulsion having a particlesize of less than about 0.6 microns.

In general, in the gel, the weight ratio of the water-insolubleorganomodified polysiloxane oil to the organomodified emulsifier rangesfrom about 0.1:1 to 10:1, preferably from about 0.1:1 to 5:1, and mostpreferably from about 0.1:1 to 1.2:1. As is generally known in the art,the amount of water that is incorporated into the gel is dependent uponthe hydrophobicity of the particular oil and the oil to emulsifierratio. For example, it is known that as the oil to emulsifier ratio islowered, the amount of water incorporated into the gel increases to afixed amount determined by the particular oil and/or emulsifieremployed. Water in excess of the fixed amount cannot be incorporatedinto the gel, and it remains in a separate aqueous phase.

When other additives are employed in the process of the presentinvention, such additives are usually present in the gel and/or finalemulsion in amounts up to about 6% by weight of the gel or of theemulsion.

Water-Insoluble Organomodified Polysiloxane Oil

The water-insoluble organomodified polysiloxane oil employed in thepresent invention is more particularly defined by the Formula I:

    R.sub.3 SiO(R.sub.2 SiO).sub.a (RQSiO).sub.b SiR.sub.3     (I)

wherein:

R is hydroxyl or a monovalent hydrocarbon group including alkyl, aryland aralkyl groups having no more than 10 carbon atoms. The R groups maybe the same as or different from one another, and are illustrated by OH,methyl, ethyl, butyl, hexyl, phenyl and benzyl. Of these, the loweralkyls (C₁ -C₄) are preferred. Most preferably, R is methyl. In FormulaI, the average value of a is from one up to 5000, and is usually atleast 10 and not more than 500. Parameter b is a number having anaverage value from 1 to 100, usually not exceeding 50. Preferably, theaverage value of each of a and b does not exceed 350.

The Q group of Formula I comprises one or two amino groups, and may alsocontain hydroxyl substitution. More particularly, Q has the generalFormula II:

    --(X).sub.d (X').sub.e (Y).sub.f --N(R.sup.1)(R.sup.2)     (II)

wherein:

X is an alkylene group having one to eight carbon atoms such as, forexample, methylene, ethylene, propylene or hexylene, and preferably hastwo to four carbon atoms;

X' is a divalent organic radical including alkylene of one to fourcarbon atoms (such as, for example, methylene, ethylene and propylene)or phenylene or preferably oxypropylene (i.e., --C₃ H₆ O--, the oxygenof which is bonded to a carbon atom of the Y group);

Y is a hydroxyl-substituted acyclic alkylene group of two to eightcarbon atoms and is illustrated by 2-hydroxypropylene, i.e., --CH₂CH(OH)CH₂ --, or Y is a hydroxyl-substituted cyclic alkylene grouphaving no more than eight carbon atoms as illustrated by2-hydroxycyclohexylene, i.e., ##STR1## of which the acyclic groupshaving two to four carbon atoms are preferred;

d,e, and f are zero or one provided the sum of d+e is one and the sum ofe+f is zero or two; and

R¹ and R² are independently hydrogen or an alkyl having from one toeight carbon atoms of which lower alkyls (C₁ -C₄) are preferred, or ahydroxyalkyl group having from two to four carbon atoms, or analkyleneamino group.

The alkyleneamino group within the scope of R¹ and R² of Formula II inturn has the following Formula III:

    --CH.sub.g H.sub.2g N(R.sup.3)(R.sup.4)                    (III)

wherein:

R³ and R⁴ are independently hydrogen, alkyl or hydrogen as defined abovewith reference to R¹ and R² ; and g is an integer from two to eight,preferably no more than four.

From the above, it is evident that the amino-containing group, Q, can bea mono- or diamino group of the following types where the specificgroups shown for X, X', Y and R¹ -R⁴, and the value of g are selectedfor illustrative purposes only:

--C₃ H₆ NH₂

--C₃ H₆ N(C₂ H₅)₂

--C₃ H₆ N(CH₂ CH₂ OH)₂

--C₃ H₆ N(CH₃)CH₂ CH₂ NH₂

--C₃ H₆ NHCH₂ CH₂ NH₂

--C₃ H₆ O--CH₂ CH(OH)CH₂ NH₂

--C₃ H₆ --N(CH₂ CH₂ OH)(CH₂ CH₂ NH₂)

--C₃ H₆ O--CH₂ CH(OH)CH₂ N(H)CH₂ CH₂ NH₂

It is to be understood that the amino groups encompassed by Formulas IIand III may be used in their protonated or quaternized form withoutdeparting from the scope of this invention.

The preparation of organomodified polysiloxane oils is well-known in theart. Such methods are described in U.S. Pat. No. 4,184,004 and Siliconand Silicones, E. G. Rochow, (Springer & Verlag, 1987) at page 97.

Organic Oil

Optionally, in one embodiment of the process of the present inventionthe polysiloxane oil can be replaced by an organic oil, such as, forexample, mineral oil. Organic oils suitable for use in the process ofthe present invention can include mineral oils such as those set forthin U.S. Pharmacopeia XXII, NF XVII, Jan. 1, 1990 edition (United StatesPharmacopeia Convention Inc.: Rockville, Md. 20852)and defined as"Topical Light Mineral Oil" and "Mineral Oil." In general, these mineraloils are linear or branched extreme hydrotreated and solvent refinedpetroleum oils having the general formula:

    C.sub.n H.sub.2n+2

wherein n is an integer ranging in value from about 10 to about 50. Themolecular weight of these oils can range from about 300 to 650 andpreferably is 300 to 350. The viscosity of suitable oils for use in theprocess ranges from about 10 centistoke to about 3000 centistoke andpreferably ranges from 10 to 60, most preferably from 10 to 34centistoke.

Organomodified Silicone Emulsifier

The organomodified silicone emulsifier used in the present invention isa polyether-modified polysiloxane more particularly defined by thefollowing Formula IV:

    R.sup.5.sub.3 SiO(R.sup.5.sub.2 SiO).sub.p (R.sup.5 ESiO).sub.q SiR.sup.5.sub.3                                           (IV)

wherein:

R⁵ is a monovalent hydrocarbon group including alkyl, aryl and aralkylgroups having no more than 10 carbon atoms. The R⁵ groups may be thesame as or different from one another, and are illustrated by methyl,ethyl, butyl, hexyl, phenyl and benzyl. Of these, the lower alkyls (C₁-C₄) are preferred. Most preferably, R⁵ is methyl. It is within thescope of this invention that the R⁵ group may additionally comprise anethylcyclohexylenemonoxide (i.e., ##STR2## When the latter group ispresent, it comprises only a minor portion of the R⁵ groups along thepolysiloxane chain. In formula IV, p has a value ranging from about 10to 150, preferably about 25 to 100, and most preferably, about 65 to 85. Parameter q has a value ranging from about 3 to 12 , preferably about4 to 10, and most preferably about 5 to 8.

The polyether group, E, of the polyether modified polysiloxanes used inthe present invention more particularly have the following generalFormula V:

    --C.sub.x H.sub.2x (OC.sub.2 H.sub.4).sub.y (OC.sub.3 H.sub.6).sub.z OR.sup.6                                                  (V)

in which x has a value from one to eight, and usually has a value fromtwo to four and preferably is three, y is a positive number; and z iszero or a positive number. However, the number of oxyethylene units inthe polyether chain must be sufficient to render the emulsifier watersoluble. It is to be understood that when z is a positive number, theoxyethylene and oxypropylene units may be distributed randomlythroughout the polyether chain or in respective blocks of oxyethyleneand oxypropylene units or a combination of random and blockdistributions.

The R⁶ group of Formula V is hydrogen, an alkyl group having from one toeight carbon atoms, or acyl group having from two to eight carbon atoms.When R⁶ is alkyl, it is preferably a lower alkyl (C₁ -C₄) such asmethyl. When R⁶ is an acyl group, it is preferable that it have no morethan four carbon atoms such as, in particular, acetyl,--C(O)CH₃. It isbelieved that when the OR⁶ terminal group of the polyether chain isacetoxy, some of the acetoxy groups of the amino-, polyether-modifiedpolysiloxane undergo reaction to form amide linkages.

Preferably the total molecular weight of the oxyalkylene portion of thepolyether group, E, is from about 200 to 10,000 and, most preferably, isfrom about 350 to 4,000. Thus the values of y and z can be those numberswhich provide molecular weights within these ranges. However, the numberof oxyethylene units in the polyether chain must be sufficient toprovide an aqueous cloud point of the polyether-modified polysiloxaneemulsifier of between 25° C. and 90° C., preferably between 40° C. and90° C., and most preferably between 40° C. and 70° C.

The preparation of organomodified polysiloxanes emulsifiers iswell-known in the art. One such method is described in U.S. Pat. No.4,847,398.

Alkaline Metal Salt

In the process of the present invention, an alkaline metal salt iscombined with the water-insoluble organomodified polysiloxane oil,organomodified silicone emulsifier and water. Preferably, the alkalinemetal salt is a water soluble inorganic salt of an alkali or alkalineearth metal. In a preferred embodiment, the salt is contained in ordissolved in the water prior to being combined with the oil andemulsifier. In general, the alkaline metal salt is present in themixture in an amount of at least 50 parts per million and less than10,000 parts per million (ppm), preferably about 100 ppm to 500 ppm, andmost preferably about 150 ppm to 300 ppm by weight of the mixture. Thealkaline metal of the inorganic salt can be sodium, potassium, cesium,lithium, calcium, magnesium or mixtures thereof. Of these, sodium andpotassium are preferred, with sodium being the most preferred. Watersoluble inorganic sodium salts include sodium chloride, sodiumcarbonate, sodium bicarbonate, sodium phosphate, sodium biphosphate,sodium sulfate and sodium bisulfate. Among these, the preferred sodiumsalts are sodium chloride, sodium carbonate and sodium bicarbonate, withsodium bicarbonate being the most preferred.

Water soluble inorganic potassium salts include potassium chloride,potassium carbonate, potassium bicarbonate, potassium phosphate,potassium biphosphate, potassium sulfate and potassium bisulfate. Amongthese, the preferred potassium salts are potassium chloride, potassiumcarbonate, and potassium bicarbonate, with potassium bicarbonate beingthe most preferred.

Cesium, lithium, calcium and magnesium salts such as the chloride,carbonate, bicarbonate, phosphate, biphosphate, sulfate and bisulfatesalts thereof are also employable in the process of the presentinvention but are generally less readily available and more expensive.Additionally, cesium and lithium salts are potentially toxic for someapplications.

Other Additives

Optionally, other additives such as organic emulsifiers, preservativesor biocides, water soluble pigments or dyes, fragrances, fillers, pHadjustors, and/or antifoamers or defoamers can be included in theemulsion. One or more of these additives may be added during the processof preparation or added to the final emulsion.

Examples of organic emulsifiers include, but are not limited to,Tergitol™ 15-S-3, 15-S-15 and mixtures thereof (available from UnionCarbide Chemicals and Plastics Company Inc.). While such organicemulsifiers are routinely incorporated in emulsion formulations, suchemulsifiers are not necessary in the process of the present invention.That is, emulsions prepared by the process of the present invention arestable without the addition of such emulsifiers.

Examples of antimicrobial preservatives include Phenonip™ (availablefrom NIPA Laboratories, Inc., Wilmington, Del.), Parasepts™ (availablefrom Kalama Chemical, Inc., Seattle, Wash.), Giv-Gard™ DXN (availablefrom Givaudan Corporation, Clifton, N.J.), Nuosept™ 95 (available fromNuodex Inc., Piscataway, N.J.) and UCARCIDE™ 250 (available from UnionCarbide Chemicals and Plastics Company Inc.)

Examples of pH adjustors include mineral acids such as hydrochloricacid, phosphoric acid and sulfuric acid, and/or organic acids such asacetic acid, citric acid and the like.

Examples of antifoamer/defoamer additives include, for example, asilicone antifoamer such as SAG™ 2001 available from Union CarbideChemicals and Plastics Company Inc.

Whereas the scope of the present invention is set forth in the appendedclaims, the following specific examples illustrate certain aspects ofthe present invention and, more particularly, point out methods ofevaluating the same. It is to be understood, therefore, that theexamples are set forth for illustration only and are not to be construedas limitations on the present invention. All parts and percentages areby weight unless otherwise specified.

The analytical procedure for determining a cloud point is well known inthe art. For example, a one-gram sample (emulsifier) is dissolved in99-milliliters of distilled water in a 150-ml beaker containing a 1-inchplastic coated stirrer bar. The beaker is placed on a combinationstirrer/hot plate. A 0° C.-to-100° C. thermometer is suspended in thesolution with the bulb of the thermometer placed 1/2-inch from thebottom of the beaker. With mild stirring, the solution is heated at arate of 1° C. to 2° C. per minute. The temperature at which thesubmerged portion of the thermometer is no longer visible is recorded asthe cloud point.

In the examples, particle size determination was performed using aMicrotrac Model 7995-30 (Leeds and Northrup, Pittsburgh, Pa.) whichmeasures light from a laser beam projected through a stream ofparticles. The angular distribution of the scatteredlight is a functionof particle size which is analyzed by a computer.

A Sartorius Model YTC-01L analyzer (Sartorius, Hayward, Calif.) was usedin the examples to determine the percentage of solids. The analyzer usesan infrared light source as a drying agent and a computer integratedbalance. The percentage of solids is calculated by computer using thedifference in sample weight before and after drying.

In the examples, samples were visually observed in four or eight-ouncejars for color/cast of the emulsion.

The following designations used in the Examples and elsewhere hereinhave the following meanings:

    ______________________________________                                        Polysiloxane                                                                            Structure                                                           ______________________________________                                        Oil #1    (CH.sub.3).sub.3 SiO[(CH.sub.3).sub.2 SiO].sub.250 Si(CH.sub.3).              sub.3                                                               Oil #2                                                                                   ##STR3##                                                           Emulsifier I:                                                                  ##STR4##                                                                     Emulsifier II:                                                                 ##STR5##                                                                     ______________________________________                                    

EXAMPLE 1

In order to illustrate the process of the present invention for makingan emulsion, 214.8 grams of Emulsifier I having a cloud point of 38° to42° C. and 214.8 grams of Oil #2 were charged to a three-necked roundbottom flask equipped with an air-driven stirrer, condenser, and atemperature controller. Oil #2 was insoluble in Emulsifier I. The twocomponents were blended together using the stirrer to agitate the blend.While maintaining the agitation, 623.3 grams of tap water (i.e., havingan alkaline metal salt or salts dissolved therein), 12.5 grams ofnonionic surfactant Tergitol 15-S-15 (a polyethylene glycol ether of alinear alcohol having 11 to 15 carbon atoms) and 8.6 grams of nonionicsurfactant Tergitol 15-S-3 (a polyethylene glycol ether of a linearalcohol having 11 to 15 carbon atoms) were charged to the flask.

After the above components were charged and agitated, the mixture washeated and pasteurized by maintaining the mixture at 80° C. for a periodof about 30 minutes. As the contents of the flask were heated, it wasobserved that a viscous concentrate (gel) formed as the cloud point(38°-42° C.) of Emulsifier I was reached and surpassed. The concentrateappeared to: have incorporated the Tergitol surfactants and theamino-modified polydimethylsiloxane oil without taking in much water(i.e., less than about 50% of the water was incorporated into theconcentrate).

A solids analysis was made on both the water phase and on theconcentrate phase. The water phase contained 0.6% solids and theconcentrate contained 70 to 75% solids. The flask was cooled by removingthe heating mantle and continuing to stir the contents of the flask.Upon cooling, the concentrate formed a viscous, translucent gel havingthe characteristics of an oil-in-water or water-continuous phaseemulsion. When an electric current was passed through the concentratethe measured resistance using an Ohm meter resulted in readings similarto those observed in known oil-in-water emulsions. A typicalwater-in-oil emulsion, in contrast, would show a resistance to currentflow so high that it would not be measurable with an ohm meter.

Further, during cooling the gel began to soften and disperse into thewater phase. When the temperature dropped below the cloud point ofEmulsifier I, an emulsion formed which had a fine particle sizeaveraging about 0.53 microns. Visual inspection of the emulsion as itran down the sides of a sample jar revealed that the emulsion had abluish translucent cast to it.

COMPARATIVE EXAMPLE A: CONTROL

An aliquot of the ingredients (emulsifier, oil, surfactants, and water)used in Example 1 was removed after blending but prior to heating thecontents in the flask. The aliquot was unstable and the componentsseparated. That is, a simple blending of the components of Example 1 didnot produce the desired oil-in-water emulsion.

EXAMPLE 2

The process of Example 1 was repeated, except that while maintaining a1:1 mole ratio of the Emulsifier I to Oil #2, a concentrate was preparedsuch that it contained 8.5% solids. The final emulsion had a bluish castas described in Example 1 and had an average particle size of 4.4microns.

EXAMPLE 3

The process of Example 1 is repeated, except that while maintaining a1:1 mole ratio of Emulsifier I to Oil #2, a concentrate was preparedsuch that it contained 38% solids. The final emulsion had a bluish castas described in Example 1 and an average particle size of 2.2 microns.

EXAMPLE 4

The process of Example 1 was repeated, except that, while maintaining a1:1 ratio of Emulsifier I to Oil #2, a reduced amount of water wasemployed such that the prepared emulsion contained 70.4% solids. Thefinal emulsion was a viscous, translucent gel and had a high electricalconductivity indicating that it was an oil-in-water emulsion, having aparticle size of about 0.25 microns or less.

EXAMPLES 5 THROUGH 8

In carrying out these Examples 5 through 8, Examples 1 through 4,respectively, were repeated except that Tergitols 15-S-15 and 15-S-3were omitted. These examples demonstrate that these non-ionicsurfactants are not required for emulsion preparation in the process ofthe present invention. The results are set forth in Table 1.

                  TABLE 1                                                         ______________________________________                                        Example No.                                                                             1      2     3    4    5    6    7    8                             ______________________________________                                        % Solid   41.1   8.5   38   70.4 42.0 10.1 35.7 72.3                          Particle size, m                                                                        0.53   4.4   2.2  0.25 .61  6.3  1.1  .25                           Shelf life,* mos.                                                                       9      1     9    1    3    1    9    1                             ______________________________________                                         *Shelf life is the period of time the respective emulsions were stored at     ambient temperature prior to use.                                        

EXAMPLES 9 THROUGH 11

These examples illustrate that the order of addition of the individualcomponents in the process of the present invention is not critical toformation of the resulting emulsion. Examples 9 through 11 were carriedout as described for Example 5, except that the order of addition wasvaried. In Example 9, the order of addition was oil, emulsifier, thenwater. In Example 10, the order of addition was water, emulsifier, thenoil. In Example 11, the order of addition was water, oil, thenemulsifier. There was no noticeable change in the emulsions duringprocessing or in the final products. The emulsions were stable andparticle sizes of the emulsions of Examples 9, 10 and 11 were 0.41,0.64, and 0.60 microns, respectively.

EXAMPLES B THROUGH I AND 12 THROUGH 24

Examples 12 through 24 illustrate mixing conditions for the process ofthe present invention. The emulsions of Examples B through I and 12through 24 were prepared in accordance with Example 5. A jacketed glassvessel having a circulating oil bath to heat the contents of the vesselwas used. The contents of the vessel were agitated using a variablespeed Lightning Mixer™ equipped with a 3-inch Cowles impeller. The speedof the mixer was varied in order to change the maximum shear rate. Eachexample was evaluated upon its appearance and shelf life stability.Examples B through H illustrate that below a maximum shear rate of 450sec.⁻¹, the emulsions on visual inspection had a grayish appearance andseparated soon after preparation. Emulsions (Examples 12 through 24)made at a maximum shear rate ranging from 450 to 1050 sec.⁻¹ were stableand appeared milky white with a bluish translucent cast while drainingdown the sides of a glass sample jar. An emulsion (Example I) preparedat a maximum shear rate of 1100 sec.⁻¹ or higher did not separateimmediately. However, the emulsion of Example I was stable for about oneweek and did not possess the bluish cast associated with a fine particlesize emulsion. The results are set forth in Table 2.

                  TABLE 2                                                         ______________________________________                                                  Maximum                                                             Example*  Shear Rate              Shelf                                       No.       Sec-1       Color       Life                                        ______________________________________                                        B         100         Gray        <1 day                                      C         150         Gray        <1 day                                      D         200         Gray        <1 week                                     E         250         Gray        <1 week                                     F         300         Gray        <1 week                                     G         350         Gray        <2 weeks                                    H         400         Gray        <2 weeks                                    12        450         Milky white >1 month                                                          w/bluish cast                                           13        500         Milky white >1 month                                                          w/bluish cast                                           14        550         Milky white >1 month                                                          w/bluish cast                                           15        600         Milky white >1 month                                                          w/bluish cast                                           16        650         Milky white >2 months                                                         w/bluish cast                                           17        700         Milky white >2 months                                                         w/bluish cast                                           18        750         Milky white >2 months                                                         w/bluish cast                                           19        800         Milky white >2 months                                                         w/bluish cast                                           20        850         Milky white >2 months                                                         w/bluish cast                                           21        900         Milky white >2 months                                                         w/bluish cast                                           22        950         Milky white >2 months                                                         w/bluish cast                                           23        997         Milky white >2 months                                                         w/bluish cast                                           24        1050        Milky white >1 month                                                          w/bluish cast                                           I         1100        Gray        <1 week                                     ______________________________________                                         *Particle size was not measured for these examples.                      

EXAMPLES 25 THROUGH 27 AND EXAMPLE J

The emulsions of Examples 25 through 27 and Example J were prepared inaccordance with the procedure of Example 1, except that Oil #1 replacedOil #2 and the emulsions contained varying amounts of solids level. Theresults are set forth in Table 3 below. As shown in Table 3, theemulsion of Example J was found to be unstable. It is not dear whatcaused the emulsion of Example J to be unstable. However, it istheorized that the emulsion of Example J was unstable because the mixingapparatus employed in the examples was insufficient to impart therequired agitation during heating due to the amount of water used in thepreparation of the mixture.

                  TABLE 3                                                         ______________________________________                                                                        Ability to                                                                    Conduct                                                                       Electrical                                    Example                                                                              Solids            Particle                                                                             Current                                       No.    Level   Color     Size   (microns)                                                                             Stability                             ______________________________________                                        25     49.8    Milky/    0.56   Yes     Yes                                                  blue cast                                                      26     68.3    Milky/    0.53   Yes     Yes                                                  blue cast                                                      27     73.7    Clear/    0.25   Yes     Yes                                                  blue cast                                                      J*     7.65    Milky/    22.69  Yes     No                                                   gray cast                                                      ______________________________________                                         *The emulsion was unstable after aging for about two weeks.              

EXAMPLE 28

The procedure of Example 5 was followed, except that the flask washeated to a temperature of 50° C. The contents of the flask were held atthat temperature for 30 minutes. The emulsion was an oil-in-wateremulsion of similar quality to that described in Example 5 and had amilky/bluish cast and a particle size of 0.46 microns. This exampleillustrates that fine stable oil-in-water emulsions can be readilyprepared by heating alone, i.e., without pasteurization.

EXAMPLE 29

The procedure of Example 1 was followed, except that Emulsifier IIhaving a cloud point of 73° to 81° C. was used instead of Emulsifier I.The contents of the vessel were heated to 92° C. for 37 minutes to formthe gel or concentrate phase. Upon cooling the emulsion was milky whitewith a bluish cast. Analysis of the gel resulted in a percent solidscontent of 70-75%.

EXAMPLE 30: PASTEURIZATION

An emulsion was prepared in accordance with the procedure of Example 1 .However, the emulsion was inoculated with 5 million colony-forming units(CFU) of bacteria and allowed to stand for one week. After one week, theemulsion was analyzed for sterility. The bacteria count showed that thebacteria (microbe) level was Too Numerous To Count (TNC). The productwas heated to 70° C. for 30 minutes to pasteurize the emulsion. Uponheating the emulsion broke up and formed into a gel phase and an aqueousphase. However, as the emulsion was cooled it was reconstituted by lowshear blending or mixing. Re-analysis by standard plate count forsterility showed that the emulsion was free of microbial contamination.

EXAMPLE 31: EFFECT OF ALKALINE METAL SALT

In order to illustrate the requirement that a minimum concentration ofalkaline metal salt is required, an emulsion was prepared using startingmaterials free of metal salt as follows: 41.3 grams of Emulsifier Ihaving a cloud point of 38° -42° C. and 41.3 grams of Oil #2 werecharged to a three-necked, round bottom flask equipped with anair-driven stirrer, condenser and a temperature controller. The twocomponents were blended together using a stirrer at low speed to agitatethe mixture. While maintaining the agitation, 97.4 grams of water freeof alkaline metal salt and obtained by a reverse osmosis water purifiermanufactured by Millipore Corporation, 2.5 grams of a nonionicsurfactant Tergitol 15-S-15 and 1.7 grams of nonionic surfactantTergitol 15-S-3 were added to the blend.

After the above components were charged to the flask, the mixture washeated to 50° C. When agitation was stopped and heating discontinued,the ingredients separated rapidly and there appeared to be no visualchange in the appearance of the components.

The components were again heated to 50° C. Upon reaching 50° C., therewas added slowly with continuous agitation a 0.8 wt. % aqueous solutionof sodium bicarbonate from a burret.

After 1.82 ml. of sodium bicarbonate solution were added, correspondingto 78 parts of sodium bicarbonate per million parts of mixture, theappearance of the mixture changed abruptly. A gel phase formed whichresembled the viscous concentrate or gel identified in Example 1.

Upon cooling to room temperature, the gel phase softened and dispersedinto the aqueous phase to form a milky emulsion with a bluish tint orcast and the emulsion was stable.

EXAMPLE 32: REPLACEMENT OF POLYSILOXANE OIL WITH AN ORGANIC OIL

The procedure of Example 1 was repeated, except that Oil #2 was replacedwith a mineral oil (nominally 24 centistoke) commonly identified as"baby oil" available from Johnson & Johnson Company. The mineral oilused in this example is further described as a branched paraffinicsaturated hydrocarbon oil. A milky white emulsion with a bluish cast andhaving a particle size ranging from less than 0.25 microns to over 4.0microns was produced. Photomicrographs indicated that the bulk of theemulsion consisted of small droplets (approximately 0.6 microns) with afew large droplets (approximately 4.0 microns). The emulsion was stablefor a period of about two weeks before noticeable separation began tooccur. When the emulsion of this example was applied to facial tissue ata rate of 1.5% combined silicone emulsifier and mineral oil, thesoftness of the tissue was substantially the same as for an emulsion ofExample 1; and the mineral oil treated tissue did not smear when used towipe a glass slide.

What is claimed is:
 1. A process for preparing an oil-in-water emulsioncomprising:(1) mixing and heating(i) mineral oil, (ii) a water solubleorganomodified polysiloxane emulsifier, (iii) water, and (iv) analkaline metal salt, above the cloud point of the emulsifier to form amixture; and (2) cooling the resulting mixture below the cloud point ofthe emulsifier.
 2. The process of claim 1 wherein the mixture is heatedat least 5° C. above the cloud point of the emulsifier.
 3. The processof claim 1 wherein mixing and heating is carried out sequentially. 4.The process of claim 3 wherein the alkaline metal salt is dissolved inthe water prior to being combined with the oil and the emulsifier. 5.The process of claim 4 wherein the alkaline metal salt is a watersoluble inorganic salt of an alkali or alkaline earth metal.
 6. Theprocess of claim 5 wherein the salt is selected from the groupconsisting of sodium bicarbonate, potassium bicarbonate, and mixturesthereof.
 7. The process of claim 4 wherein the mixture is mixed prior toheating and during cooling using low shear mixing, causing volumetricdisplacement of between 0.2 liter/minute/liter of mixture to 16liter/minute/liter of mixture.
 8. The process of claim 1 wherein mixingand heating is carried out simultaneously.
 9. The process of claim 1wherein mixing during heating is effected by applying agitation toimpart a maximum shear rate between about 450 sec.⁻¹ to 1050 sec.⁻¹ tothe mixture.
 10. The process of claim 1 wherein the organomodifiedsilicone emulsifier has the formula

    R.sup.5.sub.3 SiO(R.sup.5.sub.2 SiO).sub.p (R.sup.5 ESiO).sub.q SiR.sup.5.sub.3

wherein: R⁵ is the same or different and comprises a monovalenthydrocarbon group having 1 to 10 carbon atoms; p is from 10 to 150; q isa number having an average value from 3 to 12; E has the formula --C_(x)H_(2x) (OC₂ H₄)_(y) (OC₃ H₆)_(z) OR⁶, wherein x has a value from 1 to 8;y is a positive number; and z is zero or a positive number; and R⁶ is analkyl group having 1 to 8 carbon atoms or an acyl group having 2 to 8carbon atoms.
 11. The process of claim 1 wherein a minor portion of theR⁵ groups are ethylcyclohexylene-monoxide.
 12. The process of claim 1wherein the mixture contains at least one non-ionic surfactant.
 13. Theprocess of claim 1 wherein the mixture is pasteurized.